The present invention relates to a process for producing molten iron from a metalliferous feed material, such as ores, partly reduced ores, and metal-containing waste streams, in a metallurgical vessel containing a molten bath.
The present invention relates particularly to a molten bath-based direct smelting process for producing molten iron from a metalliferous feed material.
The term xe2x80x9cdirect smelting processxe2x80x9d is understood to mean a process that produces a molten metal, in this case iron, from a metalliferous feed material.
The present invention relates more particularly to a molten bath-based direct smelting process which relies on a molten metal layer as a smelting medium, and is generally referred to as the HIsmelt process.
The HIsmelt process includes the steps of:
(a) forming a molten bath having a metal layer and a slag layer on the metal layer in a metallurgical vessel;
(b) injecting metalliferous feed material and solid carbonaceous material into the metal layer via a plurality of lances/tuyeres;
(c) smelting metalliferous material to metal in the metal layer;
(d) causing molten material to be projected as splashes, droplets, and streams into a space above a nominal quiescent surface of the molten bath to form a transition zone; and
(e) injecting an oxygen-containing gas into the vessel via one or more than one lance/tuyere to post-combust reaction gases released from the molten bath, whereby the ascending and thereafter descending splashes, droplets and streams of molten material in the transition zone facilitate heat transfer to the molten bath, and whereby the transition zone minimises heat loss from the vessel via the side walls in contact with the transition zone.
A preferred form of the HIsmelt process is characterized by forming the transition zone by injecting carrier gas, metalliferous feed material, solid carbonaceous material and optionally fluxes into the bath through lances that extend downwardly and inwardly through side walls of the vessel so that the carrier gas and the solid material penetrate the metal layer and cause molten material to be projected from the bath.
This form of the HIsmelt process is an improvement over earlier forms of the process which form the transition zone by bottom injection of carrier gas and solid carbonaceous material through tuyeres into the bath which causes droplets and splashes and streams of molten material to be projected from the bath.
The applicant has carried out extensive pilot plant work on the HIsmelt process and has made a series of significant findings in relation to the process.
One of the findings, which is the subject of the present invention, is a procedure for starting up the HIsmelt process in an effective and efficient manner.
In general terms, the present invention is a procedure for starting up a direct smelting process for producing iron from a metalliferous feed material in a metallurgical vessel, which vessel includes a plurality of feed material injection lances/tuyeres, which start-up procedure includes the steps of:
(a) preheating the vessel;
(b) supplying a charge of molten iron to the vessel and forming a molten bath in the vessel,
(c) supplying carbonaceous material and flux to the molten bath and injecting oxygen-containing gas through one or more than one feed material injection lance/tuyere and combusting carbon and bath derived gas (if present) and thereby heating the molten bath and generating slag; and
(d) suppling metalliferous feed material to the vessel while continuing supply of carbonaceous material and flux and injection of oxygen-containing gas and smelting metalliferous feed material and producing molten iron and thereby completing the start-up procedure.
Preferably step (a) of preheating the vessel includes combusting fuel gas and air in the vessel. The term xe2x80x9cfuel gasxe2x80x9d is understood herein to include, by way of example only, coke ovens gas, blast furnace gas, and natural gas.
Preferably supply of carbonaceous material and/or flux in step (c) is via one or more than one feed material injection lance/tuyere.
Preferably supply of metalliferous feed material in step (d) is via one or more than one feed material injection lance/tuyere.
Preferably solids, ie any one or more of metalliferous feed material, carbonaceous material and flux, that are supplied via one or more than one feed material injection lance/tuyere are injected through the lance(s)/tuyere(s) with carrier gas.
The solids injection lance(s)/tuyere(s) may be movable during the course of the start-up procedure between lowered operative positions and raised retracted positions.
Alternatively, the solids injection lance(s)/tuyere(s) may be fixed during the start-up procedure and, by way of example, may extend through side walls of the vessel.
In a situation where the solids injection lance(s)/tuyere(s) are fixed, preferably step (b) includes injecting carrier gas without solids through the solids injection lance(s)/tuyere(s) at a flow rate that prevents molten metal penetrating the lance(s)/tuyere(s).
Preferably the start-up procedure includes an intermediate step between steps (b) and (c) of injecting oxygen-containing gas through one or more than one feed material injection lance/tuyere before commencing feed of carbonaceous material and flux in step (c) in order to combust oxidisable material in the molten bath and thereby increase the temperature of the bath.
Preferably step (d) of supplying metalliferous feed material commences when prescribed process conditions reach a predetermined threshold. Prescribed process conditions include, by way of example, any one or more of:
(i) molten bath temperature (preferably at least 1400xc2x0 C.); and
(ii) carbon concentration in the molten bath (preferably at least 4 wt %); and
(iii) post combustion levels (preferably below a level that indicates carbon saturation of the molten bath).
Preferably the vessel includes a forehearth and step (b) of supplying the charge of molten iron to the vessel includes supplying the charge via the forehearth.
Preferably pre-heating step (a) includes positioning a lid on the forehearth to minimise heat loss via the forehearth.
Preferably the start-up procedure includes cleaning the vessel prior to pre-heating step (a) to remove slag from the vessel.
Preferably the vessel includes water cooled panels that form at least part of side walls of the vessel and the start-up procedure includes spraying a castable refractory material onto the panels prior to pre-heating step (a) to reduce initial heat loss from the panels during the start-up procedure.
Preferably the castable refractory material is a high alumina spinel.
Preferably the start-up procedure includes connecting extensions to the ends of the solids injection lances/tuyeres prior to pre-heating step (a) to increase the effectiveness of solids injection during the start-up procedure when the level of the molten bath is relatively low. The extensions are made preferably from material which melts in the molten bath as the level of the molten bath increases and progressively submerges the extensions.
Preferably the molten iron supplied in step (b) includes at least 3 wt % carbon.
Preferably the molten iron supplied in step (b) includes silicon and/or aluminium and/or any other suitable like oxidisable material.
Preferably step (c) and the intermediate step between steps (b) and (c) includes injecting carrier gas at a pressure of at least 100 kPa over that in the vesselxe2x80x94as measured across the solids injection lances/tuyeres.
Preferably the start-up procedure includes increasing the flow rate of oxygen-containing gas during each of steps (c) and (d).
Preferably, step (c) includes injecting oxygen-containing gas through one or more than one feed material injection lance/tuyere at a flow rate of at least 12,000 Nm3/hr.
Preferably step (d) includes injecting oxygen-containing gas at a flow rate of at least 20,000 Nm3/hr.
Preferably the start-up procedure includes determining the time period for step (c) by monitoring the oxygen and/or carbon monoxide and/or carbon dioxide concentrations in off-gas from the vessel.
Preferably the start-up procedure includes determining the time period for the intermediate step between steps (b) and (c) by monitoring the oxygen and/or carbon monoxide and/or carbon dioxide concentrations in off-gas from the vessel.
Preferably the start-up procedure includes increasing the pressure in the vessel during step (c).
Slag material, including possibly slag material from a previous operation of the vessel, may be supplied to the vessel during step (c) to help minimise excessive oxidation of iron in the molten bath during step (c) by building up a slag layer on the bath.
Preferably slag material is supplied via one or more than one feed material injection lance/tuyere.
The metalliferous feed material may be any suitable iron-containing feed material. The preferred feed material is iron ore.
The iron ore may be pre-heated.
The iron ore may be partially reduced.
In some situations, such as where the vessel is subject to high heat losses, the metalliferous feed material may be a blend of iron ore and a highly reduced metalliferous feed material. In that event, preferably the start-up procedure includes the steps of reducing the amount of the highly reduced metalliferous feed material supplied to the molten bath, replacing this metalliferous feed material with iron ore, and continuing oxygen-containing gas injection and reaching steady-state process conditions.
The term xe2x80x9csteady-state process conditionsxe2x80x9d is understood to mean that the process operates with a target feed metalliferous material and within target heat and mass balances.
The above definition is understood in the context that the HIsmelt process relies on significant agitation of molten material in the vessel and, as a consequence, the process can be subject to considerable short term fluctuations.
Preferably the highly reduced metalliferous feed material injected in step (d) is at least 60% metallised.
More preferably the highly reduced metalliferous feed material is direct reduced iron (xe2x80x9cDRIxe2x80x9d).
Preferably the oxygen-containing gas is air with up to 50 vol % oxygen.
According to the present invention there is also provided a direct smelting process which includes the above-described start-up procedure.